1. Field of the Invention
The present invention relates to an impregnated cathode, and more particularly to an impregnated cathode with a construction comprising a cathode ring having an upper end to which an impregnated pallet is fitted and a lower end to which a cathode sleeve is fitted and a plurality of metal ribbons formed integrally with the cathode ring, each metal ribbon having an end fixed to a cathode holder, thereby capable of simplifying the manufacturing process and shortening the video producing time.
2. Description of the Prior Art
Impregnated cathodes have been mainly used in oscilloscopes which require high cathode current. Recently, they have been also applied to electron tubes which are used in televisions, since the electron tubes require high cathode current, according to the tendency of high resolution and large screen in televisions.
Referring to FIGS. 1A and 1B, there is shown an example of conventional impregnated cathode constructions. As shown in the drawings, the cathode comprises a cylindrical cathode cup 12 made of a heat-resistant metal and closed at its lower end, an impregnated pallet 11 fitted in the cathode cup 12 and having a porous heat-resistant sintered body to which an electron radiating material is impregnated, and a cylindrical cathode metal sleeve 13 having a closed upper end and mounted to the cathode cup 12 such that the closed upper end surface is in close contact with the lower end surface of the cathode cup 12. The cathode also comprises a cylindrical cathode holder 14 surrounding the cathode sleeve 13, a plurality of metal ribbons 15 adapted to fixedly maintain the cathode sleeve 13 and the cathode holder 14 and having one end fixed to the upper end surface of the cathode sleeve 13 and the other end fixed to the outer surface of the upper end of cathode holder, and a coil type heater 18 adapted to heat the interior of cathode and received in the cathode holder 14 to extend into the interior of cathode sleeve 13 such that the outer surface thereof is uniformly spaced from the inner surface of the cathode sleeve 13, the heater having an upper end being in contact with the inner surface of the upper end of cathode sleeve 13.
In the drawings, the reference numerals 16 and 17 designate fixing areas where the metal ribbons are fixed to the cathode sleeve 13 and the cathode holder 14.
Now, the operation of the conventional cathode with the above-mentioned construction will be described.
As a drive power is supplied to the heater 18 disposed in the cathode which has been assembled in an electron tube, the heater 18 emits heat, thereby causing the cathode to be heated. At this time, the heat emitted from the heater 18 is transmitted to the cathode cup 12, via the upper end surface of the cathode sleeve 13. The transmitted heat to the cathode cup 12 is then transmitted to the impregnated pallet 11, so that the impregnated pallet 11 radiates electrons, by virtue of the transmitted heat.
In the case of the above-mentioned construction, however, there is a disadvantage of increasing the video producing time, in that the heat generated from the heater 18 is transmitted to the impregnated pallet 11, via the closed surface of the cathode sleeve 13 and the closed surface of the cathode cup 12. Herein, the video producing time means the period of from the turning-on time point of the heater 18 to the time point that a video appears on an electron tube screen, as an electron is radiated from the impregnated pallet 11. In making the conventional cathode with the above-mentioned construction, the cathode cup 12 and the cathode sleeve 13 should be also accord with each other, so as to improve the heat transmission efficiency. Furthermore, the metal ribbons 15 should be fixed to the upper end surface of the cathode sleeve 13 at fixing areas 16 which has been accurately predetermined on the upper end surface. However, these works are very troublesome.